This invention relates to a cassette unit and to a fixture for loading the unit with a planar member.
In a number of practical applications, it is important that a planar member be held securely in a specified orientation while the surface of the member is being processed in a prescribed way. For example, in an electron beam exposure system (EBES) of the type described in IEEE Transactions on Electron Devices, Vol. ED-22, No. 7, July 1975, pages 385-392, a resist-coated substrate to be patterned is mounted on a motor-driven table which translates the substrate in an XY plane normal to a main longitudinal axis along which a deflectable electron beam is propagated. For high-quality fine-featured processing in an EBES machine, it is essential that out-of-plane motion of the writing surface of the resist-coated substrate be less than several microns. This obviously imposes severe restrictions and requirements both on the mechanical design of EBES and on the design of the cassette units utilized to hold substrates for processing in the machine.
Accordingly, considerable effort has been directed at trying to devise a cassette unit for holding a planar member in a substantially distortion-free manner. In the course of working toward this goal it was recognized that both an improved cassette unit and an associated special fixture for loading the planar member into the unit would be required.